This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application METHOD AND APPARATUS FOR CONTROLLING POWER FOR INSTANT HEATING ROLLER filed with the Korean Industrial Property Office on Jan. 30, 2001 and there duly assigned Serial No. 4221/2001.
1. Field of the Invention
The present invention relates to an instant heating roller (IHR) for use in toner image fixing, and more particularly, to a power control method and apparatus for supplying an external source voltage to a heating resistor of an IHR.
2. Description of the Related Art
Conventional power control methods for a printing apparatus, such as a printer or copy machine, are disclosed in: U.S. Pat. No. 5,627,634 entitled xe2x80x9cImage Fixing Apparatus having a Heater Energized and Controlled by Electric Energyxe2x80x9d; U.S. Pat. No. 5,907,743 entitled xe2x80x9cImage Heating Apparatus with control for Phase Control of Alternating Currentxe2x80x9d; and U.S. Pat. No. 5,994,671 entitled xe2x80x9cImage Heating apparatusxe2x80x9d. These conventional power control methods are applied to a film-type driving instant fixing system manufactured by Canon Company (Japan), and can minimize the occurrence of flicker with reduced power consumption.
Other conventional power control methods are disclosed in U.S. Pat. No. 5,376,773 entitled xe2x80x9cHeater having Heat Generating Resistorsxe2x80x9d and U.S. Pat. No. 5,621,510 entitled xe2x80x9cImage Heating Apparatus with Driving Roller having Low Thermal Expansion Coefficient Outer Layerxe2x80x9d.
For the conventional power control methods described above, when the level of external source voltage in the form of alternating current (AC) varies, the roller of the printing apparatus cannot have a consistent fixing characteristic. For example, when the roller of the printing apparatus is an IHR having a heating resistor with a resistance which is in the range of 6-8 xcexa9 for 110-130 volts and a source voltage with a level as high as 180-230 volts, an excessive current flows through the IHR and a power input port to which the AC source voltage is applied, so that the circuit can be damaged by electric shock. In addition, a high AC current flows through the IHR, thereby causing a flicker characteristic to become more severe. The term xe2x80x9cflicker characteristicxe2x80x9d refers to a temporary drop in power supplied to neighboring circuits.
A conventional power control method capable of improving the flicker characteristic is disclosed in U.S. Pat. No. 5,376,773. However, according to this method, when power applied to the IHR is lower than a predetermined level, the quantity of heat transferred to a pressure roller made of rubber decreases. As a result, it takes much time to reach a target fusing temperature with poor fixing characteristics.
To address the above limitations, it is a first object of the present invention to provide a power control method for an instant heat roller (IHR) in which consistent power can be applied to the IHR irrespective of the level or frequency of an external source voltage, and in which the IHR can reach a target fusing temperature within a shorter period of time, minimizing the occurrence of overshoot.
It is a second object of the present invention to provide a power control apparatus for an IHR by means of which the power control method is performed.
To achieve the first object of the present invention, there is provided a power control method for an instant heating roller (IHR), and, more particularly, a method for controlling a roller voltage applied to a heating resistor of the IHR, comprising the steps of: (a) determining whether an external source voltage has a first predetermined level or a second predetermined level greater than the first predetermined level; (b) if it is determined that the source voltage has the second predetermined level, supplying the source voltage as the roller voltage to the heating resistor at intervals of a second predetermined time period until the temperature of the heating resistor measured at intervals of a first predetermined time period reaches a predetermined target fusing temperature; and (c) if it is determined that the source voltage has the second predetermined level, supplying the source voltage as the roller voltage to the heating resistor for a third predetermined time period at every half period of the source voltage until the temperature of the heating resistor measured at intervals of the first predetermined time period reaches a predetermined target fusing temperature. Furthermore, as the temperature of the heating resistor approaches the predetermined target fusing temperature, the second predetermined time period is increased in step (b) and the third predetermined time period is decreased in step (c), and the first predetermined time period is equal to or greater than the second predetermined time period.
To achieve the second object of the present invention, there is provided a power control apparatus by means of which the power control method for the IHR is implemented. The apparatus comprises: a power input unit for providing an external source voltage; a voltage determination unit for determining the level of the source voltage input from the power input unit, and for outputting the result of the determination; a temperature measuring unit for measuring the temperature of the heating resistor, and for outputting the measured temperature; a first comparison unit for comparing the measured temperature and the first predetermined temperature, and for outputting the result of the comparison; a second comparison unit for comparing the measured temperature and the predetermined target fusing temperature, and for outputting the result of that comparison; a third comparison unit for comparing the measured temperature and the second predetermined temperature, and for outputting the result of that comparison; a fourth comparison unit for comparing the measured temperature and the third predetermined temperature, and for outputting the result of that comparison; a controller for outputting a power control signal in response to the results of the comparisons from the first, second, third, and fourth comparison units, and the result of the determination input from the voltage determination unit; and a power supply unit for supplying the source voltage, which is input through the power input unit, as the roller voltage to the heating resistor in response to the power control signal.